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SN74LVC1GX04: Input Capacitance at the X1 Terminal

Max Schleger
Prodigy 50 points

Part Number: SN74LVC1GX04
Other Parts Discussed in Thread: SN74LVC1GU04,

HI,

To calculate my Load Capacitance correctly i should know the input capacitance of this IC at the X1 port.

In the Data sheet i just found the Ci value and I hope that this is applies to both terminals.

Can somebody provide this Information to me
Because I can't find it on the Data sheet.

Thanks
Max

  • 0
    TI__Guru* 97676 points

    Hi Max and welcome to the forums!

    The typical input capacitance for the unbuffered input (X1 port) is 7pF. I verified this value from the SN74LVC1GU04 datasheet, since the 'X04 is just an internal combination of the 'U04 (unbuffered inverter) and the '04 (buffered inverter) designs. The '04 has an input capacitance of 3.5pF, but it doesn't really matter since it's isolated by Rs from the crystal and is directly driven from the output of the 'U04 driver -- probably why it was left out of the datasheet.

    The reason for the difference is that the buffered inverter uses smaller MOSFETs on the input stage to reduce the capacitive load and larger MOSFETs on the output stage to provide the required drive current, while the unbuffered inverter only has one stage, so it has to use larger MOSFETs to produce the desired output drive current and those larger FETs inherently have larger capacitance.

  • 0 in reply to Emrys Maier
    Prodigy 50 points

    HI Emrys,

    did you meen in output insted of in put in the sentences ?

    "The '04 has an input capacitance of 3.5pF,"

    Thanks
    Max

  • 0 in reply to Max Schleger
    TI__Guru* 97676 points

    Hey Max,

    No, I said what I meant.

    The input of the bufferd inverter ('04 function) has an input capcitance of 3.5pF.

  • 0 in reply to Emrys Maier
    Prodigy 50 points

    Ok,

    Do You know how big the output capacitance of the SN74LVC1GX04 is because I need both to calculate my load capacitance correctly.

    Cheers

    Max

  • 0 in reply to Max Schleger
    TI__Guru* 97676 points

    No, the output capacitance is not characterized. I would use 5pF for calculations.